The basic image-forming process of color photography comprises exposing a silver halide photographic recording material to light, and chemically processing the material to reveal a useable image. The fundamental steps of this processing typically entail: (1) treating the exposed silver halide with a color developer wherein some or all of the silver halide is reduced to metallic silver while an organic dye is formed from the oxidized color developer; and (2) removing the silver metal thus formed and any residual silver halide by the desilvering steps of bleaching, wherein the developed silver is oxidized to silver salts, and fixing, wherein the silver salts are dissolved and removed from the photographic material. The bleaching and fixing steps may be performed sequentially or as a single step, which is discussed herein as blixing. In some methods of color image formation, additional color or black & white development steps, chemical fogging steps and ancillary stopping, washing, accelerating and stabilizing steps may be employed.
In many situations, the useable image is provided to a customer by a multi-stage method which involves exposing a light sensitive originating element to a scene, and developing and desilvering that originating element to form a color image. The originating element may, for example, be a color negative film or a motion picture negative film. The resultant color image is then used to modulate the exposure of a light sensitive display element, with optional enlargement, in a printer. The display element may, for example, be a color paper, an intermediate film, or a motion picture projection film. The exposed display element is then developed and desilvered to form a useful color image which duplicates the original scene.
Originating elements are typically designed to allow good exposure with available light under a wide variety of lighting conditions, that is, good sensitivity (speed/grain) and dynamic range (long latitude and low gamma) are desired. Conversely, display elements are typically designed so as to allow a full range of density formation after well defined exposure and process conditions in a printer, that is, good image discrimination (high density and low fog), low dynamic range (short latitude and high gamma) and easy and consistent processing are desired. These greatly different needs are typically met by providing originating and display elements that differ markedly in silver halide content and composition as well as in the layer orders and types and quantities of image forming chemicals employed in each. One major difference in composition is evidenced in the use of silver iodobromide emulsions in the originating element, a color negative film for example, for their high sensitivity and desirable image structure properties and the use of silver chloride or silver chlorobromide emulsions in the display element, a color paper for example, for their low sensitivity, short latitude and good developability, as well as their ease of reproducible desilvering.
Silver chloride emulsions are generally known for their rapid development properties. Once reduction of silver has started, the silver chloride will rapidly reduce to silver in most common photographic developers. The problem with silver chloride emulsions in originating elements has been that the initiation of development or the latent image detection that precedes the rapid development is slow, thus silver chloride emulsions tend to have low sensitivity with high gamma. While these characteristics are suitable for print materials, camera origination materials, as already noted, must be highly sensitive and have a long latitude with relatively low gamma such as a typical color negative film. Silver chloride emulsions can only achieve the low gamma and long latitude when they are developed for very short times or in very weak developers. These short development times do not appear to be sufficient to detect the latent image of the grains receiving the least exposure, thus the sensitivity is very low when the gamma and latitude are at the desired level.
What is needed is a method of developing high chloride silver halide originating photographic elements which takes advantage of the high speed development potential of silver chloride emulsions while still providing the sensitivity, gamma and latitude requirements of such an element.